Abstract: but in comparison with the properly matured control, the grain yield of the treated plants was reduced because of the poor grain filling. This paper discusses the physiological basis of the ripening-promoting effect of Ethrel According to the experimental results, the acceleration of metabolic activity during the maturity period is one of the physiological causes of the ripening effect. Spraying Ethrel during the heading period of rice promoted the hydrolysis of carbohydrates in the vegetative organs and strengthened the synthesis in the reproductive organs. In the rice grain, the activity of phosphatase was enhanced, and the rate of starch accumulation accelerated. On the other hand due to the enhancement of the protein and chlorophyll degeneration in the functional leaf, and the decrease of photosynthetic rate, the plant community showed senescence. Moreover, the in- crease of the respiratory rate in the functional leaf increased the wasting away of dry matter and energy, as a result, the rice grain was lighter than that of the control. As with fruits of other plant species, the respiratory climacteric of the grains of the treated rice plants was advanced during the ripening process, this is also considered as one of the important physiological expressions of the ripening-promoting effect of Ethrel.